Manufacture of bituminized fibrous webs



Patented Nov. 22, 1932 UNITED STATES PATENT oFFIc E GEORGE A. RICHTER AND EIENRY AJCEASE, 0F BERLIN, NEW HAMPSHIRE, ASSIGNOBS BROWN COMPANY, OF BERLIN, NEW HAMPSHIRE, A. CORPORATION OF MAINE MANUFACTURE OF BIT'U'MIIN'IZEDv WEBB ll'o Drawing.

This invention relates to bituminized fibrous webs intended for roofing, flooring, building, and analogous purposes. It deals more especially with an article whose fibrous base is made up of water-laid, interfelted fibers and which carries a continuous phase of asphalt or equivalent bituminous Waterproofing material. p

In making bituminized sheet material, it is generally the practice to start with a fibrous felt prepared on' paper-making machinery and to pass the felt through one or more baths of molten asphaltunder conditions to ensure a uniform impre without scorching or otherwise injuring the fibers. Heretofore, cheap rags have largely constituted theraw material for making the felt, which was prepared with a view toward securing sufiicient strengthto enable the felt to be carried through the impregnating machine as a continuous sheet without rupture or breakage. v

We have found that it is possible to use a preliberated cellulose pulps of the character of the chemical wood pulps, and more especially preliberated, alkali-refined wood pulps, in preparing the web or sheet to be impregnated with molten asphalt, and to secure sur-' prisingly improved results whenvthe web is prepared on a machine of the paper-making type to possess a particular compactness, in some instances, a minimum compactness compatible with maintaining the integrity of the web when it is carried continuously through an impregnating machine. The use of refined wood pulps in particular makes possible a strikingly advantageous bituminized sheet, especially as regards the quality of high resistanceto tear, In order to secure the kind of .web which we desire, the chemical wood pulp should-be used in substantially unbeaten or in only lightly beaten or hydrated condi tion and the web should be made under a controlled application of pressure at both the wet and dry ends of thepapet machine leading to a dry web having a compactness falling within the range of about 30 to 55. These values of compactness are obtained by dividing the basis weight in pounds by the thickness in inches, and multiplying by the factor ation of the fibrous structure Application fled October '20, 1931. Serial No. 579,034.

10". The expression basis weight as lmown in papermaking circles represents the weight in pounds of 480 sheets whose dimensions are 24 x 36 inches, this being equivalent to 2880 square feet of sheet material. In other words, the compactness value really represents the weight of fiber per unit volume of sheet material.

The webs which we produce are highly absorptive in the sense that they can quickly absorb a large amount of molten asphalt or equivalent bituminous waterproofing material. Thus, they need remain immersed in the molten asphalt a shorter period of time than the felts heretofore produced, and yet imbibe asphalt amounting to 250% to 325% or in the, finished product and reduces the cost of the finished product on a poundage basis, because asphalt is considerably cheaper than fibre. Again, the texture of the web coupled with the continuous asphalt phase carried thereby gives rise to a product which can be nicely molded, as'about a'sharp-edged cubical corner, and which has remarkable re,- sistance against tearing, especially against the initiation-of tear.

While our invention comprehends the 11seof various kinds of chemical wood pulp, such as kraft and sulphite, nevertheless, we prefer to use a refined wood pulp, that is, one having, or refined to, an alpha cellulose content of at least about 93%, as the raw material for preparing our web or base composed of interfelted fiber. This preference for a refined wood pulp arises from the fact that within the limits of compactness hereinbefore given, a refined wood pulp has surprisin ly high absorptivity, and further fromthe %act that a refined wood pulp is resistant to deterioration under the degree of heating necessary for maintaining asphalt or equivalent bituminous material in a molten state and at a fluidity attended by rapid impregnation of the web. Important, too, is the fact that re--- fined wood pulp yields a waterlaid web or felt which upon being bituminized has surprisingly high resistance to tear.

A specific example of procedure .falling within the purview of the present invention may be practiced substantially as follows. A web of interfelted fiber having a compactness of about 40 and prepared from refined Wood pulp having an alpha cellulose content of at least about 93% may be used as the starting sheet. The Web may be bituminized by running it as a continuous sheet through one or more baths of molten, air-blown asphalt having a melting point of about 150 F. (ball and ring test) and heated to about 300 to 350 F.

The stretch of web in contact with the fluid sessing a dry surface, that is one free from superfluous asphalt, after the continuous phase carried by the web has been allowedor caused to congeal or set. Impregnation may be carriedout under other conditions, but in each case the contact of Web with the fluid asphalt is coordinated with a web speed suchthat a uniformly and completely lmpregnated product is secured.

Among the advantages possessed by our product is its high moisture and weather endurance to the product. The fibers are so resistance, which is traceable to the high proportion of asphalt present therein as acoutinuous phase. Indeed, the fibrous web can be said to be embedded as a skeletal reinforcement in the asphalt phase, imparting the qualities of high tear resistance and folding completely protected by the asphalt that a product containing even unrefined chemical Wood pulp, such as kraft or sulphite, as the fibrous element, stands up remarkably against the action of moisture and weathering. A product containing a refined wood pulp of an alpha cellulose content of at least about 93%, as the fibrous element, is of even greater durability both by virtue of the complete encasement of the fibers by asphalt and the high stability of the fibers. It is also possessed of a tear resistance conspicuously greater than a product containing a cotton or rag felt base,

' being, in fact, practically tear-proof.

Our invention makes possible the use of chemical wood pulp, a raw material which is available in abundance in practically all localities, in economically producing high grade bituminized webs for roofing, flooring, building, and analogous purposes. Heretofore, chemical wood pulps were regarded as inferior or unsatisfactory raw materials, partly because of their short fiber length and partly because it was assumed that bitumimzed webs possessing the requisite characteristics could not be prepared therefrom. We

. which we prepare and use as' the carrier sheets for the asphalt, lead to superior products. Our unimpregnated webs, to be sure, may be initially much weaker than the felts heretofore used, but this does not militate against their impregnation with molten asphalt as a continuous process. Evidently our webs are so highly absorptive, to begin with, that they imbibe suflicient asphalt immediately upon contact with the bath of molten asphalt,to be enormously strengthened and thus to endure the further stresses incident to being impregnated as continuous sheets without danger of being ruptured.

This application is a continuation in part of our application, Serial No. 555,232, filed August 5, 1931, which in turn,-is a continuation of our application, Serial No..198,747, filed June 14, 1927. As pointed out in those applications, the refined pulps used in forming the felt base of the bituminized sheets of the present invention are prepared by refining chemically preliberated, cellulose pulp with alkaline liquors as disclosed, for instance,in'application Serial No. 716,154, filed May 27, 1924, by George A. Richter and Milton O. Schur, and in application'Serial No. 73,193, filed December 4, 1925, by George A. Richter. In attaining the compactness values desired in the felts and more particularly those values at the lower end of the range hereinbefore given, it may, as already indicated, be necessary to dispense practically entirely with the use of pressure devices on the papermaking machine. This is especially true when the pulp used as raw material is a refined sulphite pulp whose refinement has been brought about in hot, comparatively dilute, alkaline liquors, as disclosed in the afore-mentioned Richter and Schur application Serial No. 716,154. Felts of such low compactness are of great value in making bituminized sheets for roofing and analogous purposes, where a maximum bitumen or asphalt content is desired. On the other hand,

tively col concentrated alkaline liquors, as

' disclosed in the aforementioned Richter application Serial No. 73,193, the felts fabricated from such pulp tend to be bulkier and may hence require more or less compacting or condensing during fabrication, particularly when felts whose compactness values lie at the upper end ofthe range hereinbefore given are sought. Felts whose compactness lie at the upperend of the range are of great value In making bituminized sheets for fioorings, where high moulda'bility, stretchability, and yieldability under distorting or denting influences are undesirable qualities. While it is posslble to use bleached or unbleached refined pulps in making the felts, we do not herein claim specifically the use of unbleached pulps,

as this constitutes a separate invention disinches and multipl ing by the factor 10", and

closed and claimed in application Serial No. bituminizing the elt.

580,496, filed December 11, 1931, by George A.

Richter. Bituminized sheets made in accordsignatures.

ance with the present invention are characterized by a highly desirable combination of characteristics attributable to the refined but principal raw material are, as already ind1- cated, possessed of a tear resistance conspicuously greater than a roduct contalning a cotton or rag felt base, eing, in fact, practically tearproof.

, What we claim is:

1. As an article of manufacture, sheet material for roofing, flooring, building, and analogous purposes, comprising a water-laid, fibrous base containing as an essential ingredient substantially unbeaten, wood pulp fibers whose alpha cellulose content is at least about 93%, said fibrous base having a compactness falling within the range of about 30 to 55 as determined by dividing its basis weight in pounds by its thickness in inches and multiplying by the factor 10", and said sheet carrying substantially uniformly distributed through its pores and interstices a continuous phase of asphalt .in amount of at East about 250% based on the dry weight of r. 2. As an article of manufacture, a bituminized, water-laid felt containing as an essential ingredient. substantially unhydrated, preliberated, cellulose pulp having an alpha cellulose content of at least about 93%.

3. As an article of manufacture, a bituminized, water-laid felt containin as an essential ingredient substantially un ydrated, refined wood pulp having an alpha cellulose content of at least about 93%.

4. A process which comprises-refining preliberated cellulose pulp in alkaline liquors to an alpha cellulose content of at least about felt. a

6., A process which comprises refining chemical wood pulp in an alkalineliquor to In testimony whereof we have afiixed our GEORGE A. RICHTER. HENRY A. CHASE. 

